By Andrew Gray

BRUSSELS, June 29 (Reuters) - NATO members are closing in on a compromise on Ukraine's membership aspirations that may set out how Kyiv could join the military alliance, the U.S. ambassador to NATO said on Thursday.

Ukraine has been pressing NATO to declare at a summit in Vilnius, Lithuania, on July 11 and 12, that Kyiv will join the alliance soon after the war triggered by Russia's invasion comes to an end and to set out a roadmap to membership.

The U.S. ambassador, Julianne Smith, said she was confident North Atlantic Treaty Organization would agree on a text that went beyond a declaration in Bucharest from 2008, which said Ukraine would join the alliance but did not say when or how.

"Most of us feel confident that we are going to be able to come to an agreement that will reflect where we are and that the Ukrainians will believe and feel is something above and beyond restating Bucharest," Smith told reporters.

Kyiv has received vocal support from NATO members in eastern Europe, who have argued that bringing Ukraine under the alliance's collective security umbrella is the best way to deter Russia from launching another attack on its neighbour.

But other members such as the U.S. and Germany have been more cautious, wary of any moves they fear could take the alliance closer to an active war with Russia, which has long seen NATO's expansion as evidence of Western hostility.

They have not endorsed proposals for timelines or target dates for Ukrainian membership, arguing the focus should be on repelling Russia's invasion, which Moscow calls a "special military operation".

Smith said the text on Ukraine, to be issued as part of a communique at the Vilnius summit, was still under negotiation and she declined to share precise language.

But asked if it could address the question of how Ukraine would join the alliance, she replied: "It could, yes. I think that's possible."

Smith said the text could be agreed before the summit, to which Ukrainian President Volodymyr Zelenskiy has been invited. (Reporting by Andrew Gray, Editing by Charlotte Van Campenhout and Andrew Heavens)